| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 94 === The inertial impaction and diffusion are two major mechanisms that cause particle loss in the orifice. The impaction loss in the orifice has been studied in the past. In this study, experiment was conducted using orifice with conical inlet to reduce the particle loss to study the effect of inertial impaction and diffusion. The orifice used is O’Keefe E-9, 0.455slpm orifice.
The experimental results reveal that when the flow rate through the orifice reach the critical flow rate, the penetration efficiency decreases for the particles with Dpa>457.7nm when the particle size increases more than 457.7nm or the pressure after the orifice decreases. For particle Dpa=856.8nm, the penetration is 83.2% (the pressure after the orifice is 395torr). When the conical inlet is used before orifice, it is found that the penetration efficiency is higher than that to the E-9 orifice for particles with Dpa>457.7nm. The penetration efficiency using conical inlet improves to 92.5% for particle with Dpa=856.8nm. The use of the E-9 orifice with the conical inlet may reduce the inertial impaction of the particle in the inlet of the orifice.
Secondly, when the flow rate through the E-9 orifice is smaller than the critical flow rate, the diffusion loss of the particle with Dpa<126.1nm increases with decrease in flow rate and decrease in particle diameter Dpa. The penetration efficiency for particle with Dpa=27.6nm are 80.4 % and 72.4 % with the =Q 0.357slpm and 0.242slpm, respectively. The result reveals that E-9 orifice with conical inlet can sufficiently reduce the range of the ’’recirculating zone’’. So the diffusion loss of the particle is decreases (and penetration efficiency increases). When Dpa=27.6nm, the penetration efficiency are 93.3%(Q=0.357slpm) and 83%(0.242slpm).
The result shows that the flow condition is critical flow, the pressure after the orifice reduces, the penetration efficiency of the large particle also reduces. when Dpa=856.8nm, the penetration efficiency to the E-9 orifice with conical inlet is from 92.5%(pressure after the orifice is 395torr) reduces to 59%(pressure after the orifice is 220torr). As the pressure after the orifice is decreased, the inertia of particle is increased. Thus more particles cross the centerline and impacts on the wall.
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